The present invention relates to a gas turbine which supplies and discharges a cooling medium to and from a high temperature section of the gas turbine.
Recently, a high temperature gas turbine has been developed and improved, and the temperature of the gas turbine is becoming 1500.degree. C. or more from a temperature ranging from 700.degree. C. or 900.degree. C. to 1000.degree. C. or 1300.degree. C. in the prior art technology.
Under such circumstances that the temperature of the gas turbine is rapidly made high, a superalloy steel (heat resisting alloy steel) has been developed, and the superalloy steel has applied to a high temperature section such as a turbine stationary blade and a turbine rotor blade of the gas turbine. However, the superalloy steel has exceeded its usable limit, and for this reason, there has been employed an air cooling technique of compensating for lack of material strength with the use of air. Further, in a recent gas turbine, in order to achieve a high power generation and a high heat efficiency of the gas turbine, there is a plan to make 1500.degree. C. or more a gas turbine combustion gas temperature (gas turbine inlet combustion gas temperature). In the case where a test (trial) calculation of plant heat efficiency is made with the use of the air cooling technique applied, a disadvantage occurs therein, and for this reason, a cooling medium is transferred from the air to a steam.
There have been proposed many gas turbines which use a steam as a cooling medium and one example of such gas turbines is disclosed in Japanese Patent Laid-Open Publication No. HEI 8-277725, in which FIG. 1 shows an general arrangement of the gas turbine composed a compressor, a combustor and a turbine main body including a plurality of rotors formed with discs and movable blades arranged in stages along an axial direction of the gas turbine.
As shown in FIG. 17 and FIG. 18, a steam supply passages 3 and steam recovery passages 4 are formed in a gas turbine disc 2 molded integrally with a gas turbine rotor 1 which is formed in a sectional type, a plurality of the gas turbine rotors being arranged in an axial direction thereof. A steam supplied from a rear shaft (not shown) is supplied to a gas turbine rotor blade 6 with the use of a cavity 5, and then, is cooled, and thereafter, the steam is recovered to the rear shaft via the recovery passage 4.
Meanwhile, as shown in FIG. 19, in the gas turbine, the gas turbine disc 2 including a final stage gas turbine rotor blade 6 is provided with a rear shaft 8, and a partition 14 is formed so as to divide an interior of the rear shaft 8 into the steam supply passage 3 on the center side and the steam recovery passage 4 on the opposite side. Further, the rear shaft 8 is provided a journal bearing 12 which includes a bearing housing 9, a pad 10, a retainer 11 or the like, at the outer side thereof, and is provided with a recovery pipe 13 for recovering a steam.
As described above, in Japanese Patent Laid-open Publication No. HEI 8-277725 shown in FIG. 17, FIG. 18 and FIG. 19, the cooling steam is supplied and discharged by way of the rear shaft 8 so as to reduce a thermal stress generated in the gas turbine rotor 1, the gas turbine disc 2 and the gas turbine rotor blade 6, and thus, it is possible to cope with the gas turbine from being made high temperature. Incidentally, in FIG. 18, a portion shown with oblique lines is a stacking bolt hole 7 for fixing the gas turbine disc 2 which is formed in a sectional type.
In the arrangement of the Japanese Patent Laid-open Publication No. HEI 8-277725 shown in FIGS. 17, 18 and 19, a temperature of the cooling steam supplied to the high temperature section of the gas turbine and a temperature of the recovery steam are respectively set to 250.degree. C. , and 450.degree. C. in order to restrict the temperature of these steams less than the allowable temperature of each material of the gas turbine rotor 1 and the gas turbine disc 2.
However, both the temperature 250.degree. C. of the cooling steam supplied to the high temperature section of the gas turbine and the temperature 450.degree. C. of the recovery steam far exceeds a allowable temperature of the journal bearing 12 supporting the rear shaft 8.
In general, in the journal bearing 12, a temperature of each metal component is restricted so as to be 100.degree. C. to 150.degree. C. even if a radiation heat of gas turbine combustion gas is added to a radiation heat of lubricating oil. However, in the case where the cooling and recovery steam temperatures are high, white metal adhered on a sliding surface of an inner ring of the bearing is melted, and for this reason, there is the possibility that the gas turbine falls into a dangerous state during operation.
Therefore, in the gas turbine, the steam temperature required for cooling the high temperature section of the gas turbine is secured, and there is the need of taking measures for stably operating the journal bearing 12.